1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus which forms an electrostatic latent image on an electrophotographic photosensitive member through an electrophotographic process and visualizes the electrostatic latent image with a developer contained in a developing device, and more particularly to an electrophotographic image forming apparatus having developer amount detecting means capable of sequentially detecting the remaining amount of developer contained in a developer container, a process cartridge and a developing device,.
The electrophotographic image forming apparatus is directed to, for example, an electrophotographic copying machine, an electrophotographic printer such as an LED printer or a laser beam printer, an electrophotographic facsimile machine and an electrophotographic word processor.
The process cartridge makes at least one of charging means, developing means and cleaning means and an electrophotographic photosensitive member integrally into a cartridge which is detachably mountable to a main body of the electrophotographic image forming apparatus, or makes at least the developing means and the electrophotographic photosensitive member integrally into a cartridge which is detachably mountable to a main body of the electrophotographic image forming apparatus.
2. Related Background Art
Up to now, in an image forming apparatus using an electrophotographic image forming process, there has been applied a process cartridge system which makes the electrophotographic photosensitive member and process means that acts on the electrophotographic photosensitive member integrally into a cartridge which is detachably mountable to a main body of the electrophotographic image forming apparatus. The process cartridge system can remarkably improve the operability since the maintenance of the apparatus can be conducted by a user per se not depending on a service man. For that reason, the process cartridge system has been widely employed in the electrophotographic image forming apparatus.
In one type of the electrophotographic image forming apparatuses of the above process cartridge system, a user per se can exchange the cartridge. Therefore, there includes one having means for informing the user of a fact that the developer has been consumed, that is, a developer amount (presence and absence) detecting device.
The details will be further described. FIG. 14 shows an example of an image forming apparatus A to which a conventional process cartridge B is mounted. A developing device 10 which constitutes developing means by the process cartridge B includes a developer container 11 having a developing portion 13 which supplies a developer T to a latent image formed on a photosensitive drum 1 serving as an image bearing member to visualize the latent image and a hopper portion 14 provided for the purpose of reserving and storing the developer T. Then, the developer T within the hopper portion 14 is fed to the developing portion 13 from the interior of the hopper portion 14 through the gravity and an agitating device 15 or other developer feeding means.
In the developing portion 13, a developing roller 12 that serves as a developer bearing member for feeding the developer T up to a developing position opposite to the photosensitive drum 1 is disposed in the vicinity of the photosensitive drum 1. The developer T is stuck and borne on the surface of the developing roller 12, and the developer T is fed up to the developing position opposite to the photosensitive drum 1 due to the rotation of the developing roller 12.
The amount and height of the developer T are regulated and uniformly coated on the developing roller 12 by developer regulating means 17 such as a doctor blade while the developer T is being fed. The developer T is rubbed by the developing roller 12, the developer regulating means 17 or the developer T per se so as to be charged during a process where the developer T is fed onto the developing roller 12.
Then, the developer T fed to a portion of the developing roller 12 opposite to the photosensitive drum 1 by the developing roller 12, that is, to a developing position in which the developer T is transferred onto the photosensitive drum 1 due to an appropriate developing bias voltage applied between the photosensitive drum 1 and the developing roller 12 by a developing bias power supply 12A which serves as bias applying means, and an electrostatic latent image on the photosensitive drum 1 is then developed to form a toner image.
The developer T which has not been used for development is fed while it remains on the developing roller 12, and then again contained in the developing portion 13.
On the other hand, a recording medium P set in a sheet feeding cassette 20 is conveyed to a transfer position by a pickup roller 21 and conveying means 22 having a conveying roller pair, a registration roller (not shown) and so on in synchronism with the formation of the toner image. A transfer roller 4 is disposed as transfer means at the transfer position, and the toner image on the photosensitive drum 1 is transferred onto the recording medium P by application of a voltage.
The recording medium P to which the toner image has been transferred is conveyed to fixing means 5 by a conveying guide 23. The fixing means 5 includes a driving roller 5c and a fixing roller 5a having a heater 5b therein which applies heat and pressure to the recording medium P which is passing through the fixing means 5 to fix the transferred toner image onto the recording medium P. Thereafter, the recording medium P is discharged to the external of the apparatus.
The photosensitive drum 1 after the toner image thereon has been transferred onto the recording medium P by the transfer roller 4, is subjected to a succeeding image forming process after the developer remaining on the photosensitive drum 1 has been removed by cleaning means 6. The cleaning means 6 scrapes off the residual developer on the photosensitive drum 1 by an elastic cleaning blade 7 disposed so as to be abutted against the photosensitive drum 1 and collects the residual developer into a waste developer reservoir 8.
As described above, in the developing device 10, because the developer T is consumed every time the developing operation is repeated, it is necessary to monitor the presence and absence of the developer T in the developing portion 13 at any time so as to prevent the shortage of the developer T.
Since the developer T is contained within the developer container 11 of the developing device 10, the user cannot recognize the residual amount of developer T from the outside using his eyes.
Under the above circumstances, the conventional developing device 10 includes a developer amount detecting device as near-end detection means for detecting the residual amount of the developer, and the developer amount detecting device includes a bar-shaped antenna electrode 18 for detection of the residual amount of the developer which is disposed horizontally in the interior of the developing portion 13 in order to detect the residual amount of the developer T.
As described above, there has been applied a system in which an alternate (a.c.) bias voltage from the developing bias power supply 12A is applied to the developing roller 12 when the image is formed, and in this situation, the developer amount detecting device detects an electric current that flows in the antenna electrode 18 by the a.c. bias voltage. That is, the detection of the developer residual amount utilizes a change in the capacitance due to the amount of developer that is interposed between the developing roller 12 and the antenna electrode 18.
That is, the current that flows in the antenna electrode 18 gradually changes as the developer T contained in the developer container 11 is gradually consumed every time an image is formed. Therefore, when its value reaches a given value, that time is indicated on a personal computer or an operation panel of a printer as a toner end so that information of no developer can be transmitted to the user.
As described above, the conventional developer amount detecting device is adapted to detect the presence and absence of the developer T within the developer container 11, that is, it can merely detect that the amount of developer T is small immediately before the developer within the developer container 11 is completely consumed. Thus, the conventional developer amount detecting device cannot detect the residual amount of developer T within the developer container 11.
On the contrary, if the residual amount of developer T within the developer container 11 can be sequentially detected, the user can be notified of a state in which the developer within the developer container 11 is consumed. Therefore, the user can prepare a new process cartridge at a replacement timing.
Under the above circumstances, in order to sequentially detect the residual amount of developer together with the use of the near-end detecting means, there have been proposed that the respective image signals for forming image dots are counted and multiplied by a given coefficient to detect the consumed amount of developer, or a period of time of transmitting a light emitting signal to a laser or the like which produce an electrostatic latent image is integrated to sequentially grasp the residual amount of developer.
The above combination of the developer residual amount sequential detection with the near-end detecting means makes it possible to sequentially notify the user of the residual amount of developer, and the information of no developer can be accurately transmitted to the user by the near-end detecting means.
However, in the means for sequentially detecting the developer residual amount to count the respective image signals which form the image dots as in the above conventional device, because the consumed amount of developer is different depending on the type of image, that is, between a line portion and an independent dot portion, there is a fear that an error may occur when the amount of developer is detected.
In addition, the near-end detecting means in the above conventional device can normally print 200 to 300 sheets at a printing ratio of 4% after the information of no developer has been transmitted to the user, but the specific number of printable sheets depends on an area of transfer material to be used and the printing ratio. For that reason, it is difficult to discriminate how many sheets can be printed.